The invention relates to a microwave amplifier tube having a first and a second ring resonator of which the first serves as a driver resonator and the second serves as an output resonator. By means of a cathode system an electron beam rotating around the ring axis at the frequency of a control signal is generated. The electron beam is accelerated by a direct voltage and enters the second ring resonator which is tuned to the same frequency as the first resonator. The electron beam influences a high-frequency electromagnetic field in the second resonator and delivers a part of its energy to said second resonator.
A microwave amplifier tube of this type is known from U.S. Pat. No. 4,210,845. This patent is hereby incorporated by reference to provide background information on the functioning of such highly efficient very high power microwave amplifiers.
In the known tube termed "Trirotron" a cathode provided in a ring resonator serves as a source for a radially-directed, rotating, spoke-shaped electron beam. By means of a biased grid at the emanating gap of the resonator it is achieved that electrons leave the control resonator only at the place of the rotating maximum of the electric field strength. These electrons are then accelerated by a high electrostatic field and enter the output ring resonator.
In such a microwave amplifier tube having two concentrically arranged ring resonators it is difficult to operate the resonators at the same angular phase velocity. Furthermore, in such a tube the focusing of the electron beam is difficult because the resonators are arranged concentrically with respect to each other.